sysdeps/ieee754/dbl-64/s_round.c

   1 /* Round double to integer away from zero.
   2    Copyright (C) 1997-2015 Free Software Foundation, Inc.
   3    This file is part of the GNU C Library.
   4    Contributed by Ulrich Drepper <drepper@cygnus.com>, 1997.
   5
   6    The GNU C Library is free software; you can redistribute it and/or
   7    modify it under the terms of the GNU Lesser General Public
   8    License as published by the Free Software Foundation; either
   9    version 2.1 of the License, or (at your option) any later version.
  10
  11    The GNU C Library is distributed in the hope that it will be useful,
  12    but WITHOUT ANY WARRANTY; without even the implied warranty of
  13    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14    Lesser General Public License for more details.
  15
  16    You should have received a copy of the GNU Lesser General Public
  17    License along with the GNU C Library; if not, see
  18    <http://www.gnu.org/licenses/>.  */
  19
  20 #include <math.h>
  21
  22 #include <math_private.h>
  23
  24
  25 static const double huge = 1.0e300;
  26
  27
  28 double
  29 __round (double x)
  30 {
  31   int32_t i0, j0;
  32   u_int32_t i1;
  33
  34   EXTRACT_WORDS (i0, i1, x);
  35   j0 = ((i0 >> 20) & 0x7ff) - 0x3ff;
  36   if (j0 < 20)
  37     {
  38       if (j0 < 0)
  39         {
  40           math_force_eval (huge + x);
  41
  42           i0 &= 0x80000000;
  43           if (j0 == -1)
  44             i0 |= 0x3ff00000;
  45           i1 = 0;
  46         }
  47       else
  48         {
  49           u_int32_t i = 0x000fffff >> j0;
  50           if (((i0 & i) | i1) == 0)
  51             /* X is integral.  */
  52             return x;
  53           math_force_eval (huge + x);
  54
  55           /* Raise inexact if x != 0.  */
  56           i0 += 0x00080000 >> j0;
  57           i0 &= ~i;
  58           i1 = 0;
  59         }
  60     }
  61   else if (j0 > 51)
  62     {
  63       if (j0 == 0x400)
  64         /* Inf or NaN.  */
  65         return x + x;
  66       else
  67         return x;
  68     }
  69   else
  70     {
  71       u_int32_t i = 0xffffffff >> (j0 - 20);
  72       if ((i1 & i) == 0)
  73         /* X is integral.  */
  74         return x;
  75
  76       math_force_eval (huge + x);
  77
  78       /* Raise inexact if x != 0.  */
  79       u_int32_t j = i1 + (1 << (51 - j0));
  80       if (j < i1)
  81         i0 += 1;
  82       i1 = j;
  83       i1 &= ~i;
  84     }
  85
  86   INSERT_WORDS (x, i0, i1);
  87   return x;
  88 }
  89 weak_alias (__round, round)
  90 #ifdef NO_LONG_DOUBLE
  91 strong_alias (__round, __roundl)
  92 weak_alias (__round, roundl)
  93 #endif